In-plane switching mode liquid-crystal display device and fabrication method thereof

ABSTRACT

An in-plane switching mode liquid crystal display device including a first substrate and a second substrate, data lines and gate lines arranged in a matrix form on the first substrate to define a pixel, a thin film transistor at a cross portion of the gate and data lines, a black matrix over the gate lines, data lines, and the thin film transistor, a color filter layer in the pixel, at least a pair of a common electrode and a pixel electrode over the color filter layer and a liquid crystal layer between the first and second substrates.

This application claims the benefit of Korean Application No. 2002-62144filed in Korea on Oct. 11, 2002, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) device,and particularly, to an in-plane switching mode LCD device and afabrication method thereof by which aperture ratio and the reliabilityof image quality can be improved.

2. Description of the Related Art

An LCD device of twisted nematic mode, which is mainly used in flatpanel display devices having high image quality and low powerconsumption, has a narrow viewing angle. The refractive anisotropy ofliquid crystal molecules together with the vertical orientation of theliquid crystal molecules with respect to the substrate when voltage isapplied to a twisted nematic mode LCD device causes a narrow viewingangle. In contrast, an in-plane switching mode LCD has a wide viewingangle since the liquid crystal molecules are oriented in a directionparallel to the substrate when voltage is applied to an in-planeswitching mode LCD device.

FIG. 1A is a plan view showing a pixel of a related art in-planeswitching mode LCD. FIG. 1B is a cross-sectional view along line I-I′ inFIG. 1A. As shown in FIG. 1A, gate lines 1 and data lines 3 arerespectively arranged in longitudinal and transverse directions on atransparent first substrate 10 to define a pixel. In an LCD device witha panel having pixels, n gate lines 1 and m data lines 3 are crossed tomake a panel having n×m pixels.

In the pixel, a thin film transistor 9 is formed adjacent to anintersection where one of the gate lines 1 and one of the date lines 3cross over each other. The thin film transistor 9 includes a gateelectrode 1 a, source electrode 2 a and drain electrode 2 b that arerespectively connected to the gate line 1, to the data line 3 and to thepixel electrode 7. A gate insulating layer 8 is formed above the gateelectrode 1 a. A semiconductor layer 5 is formed above the gateinsulating layer 8. The source electrode 2 a and drain electrode 2 b arerespectively formed in contact with an end of the semiconductor layer 5.

As shown in FIG. 1A, a common line 4 traverse across the pixel and is inparallel with the gate line 1. A pixel electrode line 14 overlaps thecommon line 4 as the common line 4 traverse across the pixel. Commonelectrodes 6, which branch from the common line 4, and pixel electrodes7, which branch from the pixel electrode line 14, are arranged to be inparallel with each other for switching the liquid crystal molecules. Thecommon electrodes 6 are formed simultaneously with the gate electrode 1a. The pixel electrode 7 is formed simultaneously with the both sourceelectrode 2 a and drain electrode 2 b such that the pixel electrode 7 isconnected to the drain electrode 2 b of the thin film transistor 9. Inaddition, a passivation layer 11 and then a first alignment layer 12 aare formed over the first substrate 10 including the source/drainelectrodes 2 a and 2 b.

As shown in FIG. 1B, the common electrodes 6 are formed adjacent to theperiphery of the pixel to shield the pixel electrode from a lateralelectric field generated by the data lines 3 formed on the periphery ofthe pixel. The pixel electrode line 14 overlaps the common line 4 with agate insulating layer 8 therebetween to form a storage capacitor. Ablack matrix 21 for preventing light from leaking between pixels isformed on the surface of a second substrate 20 facing the firstsubstrate 10. The black matrix 21 covers the thin film transistor 9, thegate lines 1, the data lines 3, and the common electrodes 6 adjacent tothe data lines 3 on the first substrate 10. In addition, a color filter23 with a second alignment layer 12 b thereon is also formed on thesurface of a second substrate 20 facing the first substrate 10. A liquidcrystal layer 13 is formed between the first substrate 10 and the secondsubstrate 20.

When a voltage is not applied to an in-plane switching mode LCD deviceas shown in FIGS. 1A and 1B, the liquid crystal molecules in the liquidcrystal layer 13 are oriented corresponding to the alignment directionof the first alignment layer 12 a and the second alignment layer 12 b.However, when a voltage is applied between the common electrodes 6 andthe pixel electrodes 7, the liquid crystal molecules are reoriented tobe in parallel with the substrate and vertical to the extended directionof the common electrodes 6 and the data lines 3.

The liquid crystal molecules in the liquid crystal layer 13 is alwaysreoriented on the same plane. Accordingly, gray level inversion does notappear to be generated when the panel of the LCD device is viewed fromabove, below, left or right of the LCD panel at an off angle to normalof the LCD panel. However, in the in-plane switching mode LCD devicehaving the structure shown in FIGS. 1A and 1B, in which the black matrix21 of the second substrate 20 covers the thin film transistor 9, thegate lines 1, the data lines 3, and the common electrodes 6 adjacent tothe data lines 3 on the first substrate 10, light leakage may begenerated due to a misalignment between the first substrate 10 and thesecond substrate 20. Thus, the width of the black matrix 21 has to beformed wider than the widths of the thin film transistor 9, the gatelines 1 and the data lines 3 to maintain misalignment error margin. Asthe width of the black matrix 21 is increased, the aperture ratio of theunit pixel is reduced. A decrease in the aperture ratio can reduce theresolution and brightness of the image displayed on the LCD panel of anLCD device.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an in-plane switchingmode LCD device and fabrication method thereof that substantiallyobviate one or more of the problems due to limitations and disadvantagesof the related art.

An object of the present invention is to prevent light leakage due tomisalignment of the first and second substrates in an in-line switchingmode LCD device.

Another object is to improve the aperture ratio of a pixel in anin-plane switching mode LCD device.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve the objects of the present invention, as embodied and broadlydescribed herein, there is provided an in-plane switching mode liquidcrystal display device including: a first substrate and a secondsubstrate; data lines and gate lines arranged in a matrix form on thefirst substrate to define a pixel; a thin film transistor at a crossportion of the gate and data lines; a black matrix over the gate lines,data lines, and the thin film transistor; a color filter layer in thepixel; at least a pair of a common electrode and a pixel electrode overthe color filter layer; and a liquid crystal layer between the first andsecond substrates.

In another aspect of the present invention, there is provided anin-plane switching mode liquid crystal display device includes a firstsubstrate and a second substrate, the first substrate including: datalines and gate lines arranged in a matrix form on the first substrate todefine a pixel; a thin film transistor at a cross portion of the gateand data lines, the thin film transistor including a gate electrode, asemiconductor layer, a source electrode and a drain electrode; a blackmatrix over the gate lines, data lines, and the thin film transistor; acolor filter layer in the pixel; an overcoat layer over the color filterlayer; and at least a pair of a common electrode and a pixel electrodeon the overcoat layer.

In another aspect of the present invention, there is provided afabrication method of an in-plane switching mode LCD device including:forming a gate electrode on a first substrate; forming a semiconductorlayer on the gate electrode; forming a source electrode and a drainelectrode on the semiconductor layer; forming a passivation layer on thefirst substrate; forming a black matrix above the passivation layer;forming a color filter layer above the passivation layer; and forming apixel electrode and a common electrode over the color filter layer.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIGS. 1A and 1B are views showing structure of a related art in-planeswitching mode LCD device.

FIG. 2 is a view showing a unit pixel of an in-plane switching mode LCDdevice according to a first exemplary embodiment of the presentinvention.

FIG. 2B is a cross-sectional view along line II-II′ in FIG. 2A.

FIG. 3 is a view showing an in-plane switching mode LCD device accordingto a second exemplary embodiment of the present invention.

FIGS. 4A through 4G are processing views illustrating a fabricationmethod of the in-plane switching mode LCD device according to the secondexemplary embodiment of the present invention.

FIGS. 5A and 5B are cross-sectional views showing a pad area connectinga gate line and a data line to outer driving circuits.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 2 is a plan view showing a pixel of an in-plane switching mode LCDdevice according to a first exemplary embodiment of the presentinvention. FIG. 2B is a cross-sectional view along line II-II′ in FIG.2A. As shown in FIG. 2A, gate lines 101 and data lines 103 arerespectively arranged in longitudinal and transverse directions todefine a pixel. Common electrodes 106 and pixel electrodes 107 arepositioned in parallel with the data lines 103. The pixel electrodes 107are positioned in between the common electrodes 106 with a predeterminedgap between each of the common electrodes 106 and each of the pixelelectrodes 107 in the pixel. A thin film transistor 109 is disposed inthe pixel adjacent to where one of the gate lines 101 and one of thedata lines 103 cross each other. The thin film transistor 109 comprisesa gate electrode 101 a connected to the gate line 101, a semiconductorlayer 105 formed on the gate electrode 101 a, a source electrode 102 aformed on the semiconductor layer 105 and connected to the data line103, and a drain electrode 102 b facing the source electrode 102 a andconnected to the pixel electrode 107.

The pixel electrode 107 overlaps with one of the gate lines 101 that isnot connected to the thin film transistor 109 of the pixel. Storageelectrode 130 that is connected to the drain electrode 102 b of the thinfilm transistor 109 is disposed between the common electrodes 106 andoverlaps the one of the gate lines 101 that is not connected to the thinfilm transistor 109 of the pixel. The storage electrode 130 and thepixel electrode 107 are connected through a contact hole 140 above theone of the gate lines 101 that is not connected to the thin filmtransistor 109 of the pixel. A portion of the storage electrode 130overlapping the one of the gate lines 101 that is not connected to thethin film transistor 109 of the pixel with a gate insulating layer 108therebetween forms a storage capacitor.

As shown in FIG. 2B, the gate lines 101 are formed on a transparentfirst substrate 110, and the storage electrode 130 and the data lines103 are formed on the gate insulating layer 108. In addition, apassivation layer 111 is formed over the entire surface of the substrateincluding the storage electrode 130 and the data line 103. A blackmatrix 121 is formed over an area corresponding to the gate line 101 andthe data line 103 to prevent light from leaking between pixels. A colorfilter layer 123 is formed on the black matrix 121 corresponding to thepixel. In the alternative, the color filter layer 123 may be formed onthe passivation layer 111 prior to the formation of the black matrix121. An overcoat layer 150 for flattening the color filter layer 123 isformed on the color filter layer 123. The common electrodes 106 and thepixel electrodes 107, which are disposed alternately with a certainpredetermined gap therebetween, are formed on the overcoat layer 150.One of the common electrodes 106 overlaps with the data lines 103 at theperipheral sides of the pixel. In addition, a first alignment layer 112a is formed over the common electrode 106 and the pixel electrode 107. Asecond alignment layer 112 b is formed on the second substrate 120, anda liquid crystal layer 113 is formed between the first and secondsubstrates 110 and 120.

In the LCD device having the structure shown in FIGS. 2A and 2B, thedata lines 103 and the common electrodes 106 adjacent to the data lines103 are formed to be overlapped with each other, and thereby, theaperture ratio can be improved. Also, the pixel electrodes 107 areformed on the overcoat layer 150 that is on the same plane on which thecommon electrode 106 is formed. Because the pixel and common electrodes107 and 106 are formed on the same plane, a desirable lateral electricfield is generated parallel to the surface of the substrate when avoltage is applied between the pixel and common electrodes 107 and 106.Therefore, the viewing angle is further improved. Moreover, when it iscompared to the related art, the electric field between the twoelectrodes is directly applied to the liquid crystal layer withoutpassing through the passivation layer, and therefore, stronger electricfields can be generated. The liquid crystal molecules in the liquidcrystal layer can be switched more rapidly due to a stronger electricfield, and therefore, moving pictures can be more readily realized.

Also, since the color filter layer 123 is formed on the same substrateas that of the thin film transistor 109, misalignment between the colorfilter layer and the corresponding pixel is not generated when the uppersubstrate 120 and the lower substrate 110 are attached. Therefore,attaching margin with the black matrix 121 which blocks the light can bereduced, and the aperture ratio can be improved.

In more detail, as shown in FIG. 1B, since the color filter 23 and thethin film transistor 9 are formed on different planes from each otheraccording to the related art, respective R, G and B color filters shouldbe corresponded to one pixel when the upper substrate 20 on which thecolor filter layer 23 is formed and the lower substrate 10 on which theblack matrix 21 is formed are attached. In case that these aremis-aligned, inferiority such as light leakage and color interruptionbetween pixels can be generated. Therefore, in order to prevent theinferiority, the width of the black matrix on the upper substrate shouldbe formed to be wide, and thereby, the aperture ratio is reduced.

On the contrary, according to the present invention, since the colorfilter 123 is formed on essentially the same plane as that of the thinfilm transistor 109, the attaching margin for preventing themisalignment is not needed, and thereby, the width of the black matrix121 can be reduced less than that of the related art.

FIG. 3 is a plane view showing an in-plane switching mode LCD devicehaving a storage on a common structure according to a second exemplaryembodiment of the present invention. A difference between the firstexemplary embodiment and the second exemplary embodiment is with regardto the storage capacitor formed by a common line 204 and a storageelectrode 230 formed thereon in the present embodiment. That is, asshown in FIG. 3A, a portion 201 a of the gate line 201 is disposed to bein parallel with the common line 204. The portion 201 a of the gate line201 connects to the gate electrode of a thin film transistor 209. Thestorage electrode 230, which is connected to a drain electrode 202 b ofthe thin film transistor 209, is disposed to overlap the common line204, and therefore forms an overlapped region 225 that is a storagecapacitor. Pixel electrodes 207 is also disposed on the same plane asthe common electrodes 206. Some of the common electrodes 206 aredisposed on the periphery of the pixel over the data lines 203 toincrease the aperture ratio. In addition, the pixel electrodes 207 areconnected to the storage electrode 230 through a contact hole 240.Because the storage electrode 230 is connected to the drain electrode202 b, an additional contact hole for connecting the drain electrode 202b and the pixel electrode 207 is not necessary.

FIGS. 4A through 4G are processing views illustrating the fabricationmethod of a pixel for an in-plane switching mode LCD device according toan exemplary embodiment of the present invention. As shown in FIG. 4A,after providing a transparent insulating substrate 310, such as glass, ametal, such as Cr, Ti, Cr, Al, Mo, Ta and Al alloy, is deposited on thesubstrate 310 using a sputtering method and patterned to form a gateelectrode 301 a. Gate lines connected to the gate electrode 301 a arealso formed with the gate electrode 301 a. In the case that the commonlines 204 may also be formed with the gate lines and gate electrode 301a, as shown in FIG. 3, the common lines 204 may also be formed.

Next, as shown in FIG. 4B, SiNx or SiOx is deposited on the entiresubstrate 310 using, for example, a plasma CVD method to form a gateinsulating layer 308. Then, amorphous silicon 305 a and n+amorphoussilicon 305 b are deposited and patterned on the upper part thereof toform a semiconductor layer 305. The semiconductor layer 305 is alsoformed on an area in which the data line will be formed to supply a datasignal through the semiconductor layer 305 if an open occurs in the dataline due to the inferiority of processing when forming the data line.

Next, as shown in FIG. 4C, a metal, such as Cu, Mo, Ta, Al, Cr, Ti andAl alloy, is deposited using, for example, a sputtering method andpatterned to form a source electrode 302 a and a drain electrode 302 bon the semiconductor layer 305. In addition, a part of the semiconductorlayer which is formed by the n+amorphous silicon is removed to form anohmic contact layer 305 b so as to insulate the source electrode 302 aand the drain electrode 302 b. The storage electrode connected to thedrain electrode 302 b that overlaps with the gate line may be formedwith the drain electrode 302 b. Further, the common line may be formedwith the storage electrode.

As shown in FIG. 4D, an inorganic material, such as SiOx or SiNx, or anorganic material such as BCB (benzocyclobutene) or acryl, is depositedover the source and drain electrodes 302 a and 302 b including thesemiconductor layer 305 and over the entire upper surface of the gateinsulating layer 308 to form a passivation layer 311. Then, as shown inFIG. 4E, an opaque metal material, such as Cr, is deposited on thepassivation layer 311 and patterned to form a black matrix 321. Theblack matrix is formed over the gate lines, the data lines, and the thinfilm transistor. The black matrix may be formed of resin.

As shown in FIG. 4F, a color pigment is deposited on the black matrix321 and the passivation layer 311 and patterned to form the color filterlayer 323 of an appropriate one of red R, green G and blue B colors. Inthe alternative, the color filter layer 323 may be formed on thepassivation layer 311 prior to the formation of the black matrix 321.The color filter layer 323 is formed to correspond to the respectivepixels. To form each of the R, G and B color filters, three depositionand three patterning processes are required. In addition, an overcoatlayer 350 may be formed on the color filters for flattening the colorfilters, and a contact hole for exposing a part of the storage electrodeis formed, as shown in FIG. 2B.

As shown in FIG. 4G a metal, such as Cr, Ti, Cr, Al, Mo, Ta and Al alloyare deposited over the overcoat layer 350 using, for example, asputtering method and patterned to form the common electrodes 306 andthe pixel electrodes 307. The common electrodes 306 and the pixelelectrodes 307 are formed to be in parallel with the data lines, forexample. The pixel electrodes 307 are formed to be connected with thestorage electrode through the contact hole. The common electrodes 306and the pixel electrodes 307 may be formed using an opaque metal.However, they also may be formed using a transparent conductivematerial, such as Indium Tin Oxide (ITO) or Indium Zinc Oxide (IZO).

Although it is not shown in FIGS. 4A-4G, a contact process of gate/datapad units to gate/data driver integrated circuits is made simultaneouslywith the deposition and patterning of the common electrodes 306 and thepixel electrodes 307. Therefore, when the two electrodes 306 and 307 areformed from an ITO or IZO, additional metallization processes are notrequired for connecting gate/data pad units to gate/data driverintegrated circuits. More specifically, the gate pad 301 b is formedwith the gate lines and the gate electrode 301 a on the first substrate310, and the data pad 303 b is formed with the data lines and thesource/drain electrodes 302 a and 302 b on the gate insulating layer308, as shown in FIGS. 5A and 5B. The passivation layer 311 on the pads301 b and 303 b is etched to expose the pads 301 b and 303 b so that thepads may be connected to an outer driving circuit (not shown). When thepads 301 b and 303 b are exposed to air, an oxidation layer is formed onthe surface of the pads 301 b and 303 b, and causes inferior contactingto the outer driving circuits. Therefore, as shown in FIGS. 5A and 5B,when a metal layer 330 made of ITO or IZO is formed on the pads 301 band 303 b, the oxidation of the pads can be prevented. Thus, when thecommon electrodes 306 and the pixel electrodes 307 are made of thesematerials, the metal layer 330 may be formed simultaneously.

As described above, the color filter layer is formed on the same planeas that of the thin film transistor according to the present invention,and thereby, the misalignment between the upper substrate and the lowersubstrate can be prevented and the aperture ratio can be improved. TheLCD device having the above structure includes the black matrix on thefirst substrate, and therefore, the first and second substrates may beattached without the concern of an alignment margin for the blackmatrix. Thus, the width of the black matrix can be reduced such that theaperture ratio can be improved. Also, the common electrodes and thepixel electrodes are formed on the overcoat layer such that a desirablestrong electric field is generated in parallel with the surface of thesubstrate to switch the liquid crystal layer while maintaining a wideviewing angle.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1-21. (canceled)
 22. A fabrication method of an in-plane switching modeliquid crystal display device, comprising: forming data lines and gatelines arranged in a matrix form on a first substrate to define a pixel;forming a thin film transistor at a cross portion of the gate and datalines; forming a black matrix over the gate lines, data lines, and thethin film transistor; forming a color filter layer in the pixel; formingat least a pair of a common electrode and a pixel electrode over thecolor filter layer; forming a storage electrode under the color filterlayer, the storage electrode is connected to the pixel electrode; andforming a liquid crystal layer on the first substrate.
 23. The method ofclaim 22, wherein forming the thin film transistor includes: forming agate electrode; forming a gate insulating layer on the gate electrode;forming a semiconductor layer on the gate insulating layer; and forminga source electrode and a drain electrode on the semiconductor layer. 24.The method of claim 22, wherein the storage electrode overlaps one ofthe gate lines, the storage electrode being on the gate insulatinglayer.
 25. The method of claim 22, further comprising forming anovercoat layer on the color filter layer.
 26. The method of claim 22,further comprising forming a common line in parallel with the gatelines.
 27. The method of claim 26, wherein the storage electrodeoverlaps the common line.
 28. The method of claim 26, wherein a firstportion of the common electrode overlaps the data lines.
 29. The methodof claim 28, wherein a second portion of the common electrode overlapsone of the gate lines and the thin film transistor.
 30. The method ofclaim 29, wherein a third portion of the common electrode overlapsanother one of the gate lines.
 31. The method of claim 22, wherein pixelelectrodes are formed between common electrodes with a predetermined gapbetween each of the common electrodes and each of the pixel electrodes.32. The method of claim 22, further comprising forming a gate pad and adata pad on the first substrate.
 33. The method of claim 32, wherein thegate pad and data pad include one of Indium Tin Oxide (ITO) and IndiumZinc Oxide (IZO).
 34. The method of claim 31, wherein the pixelelectrodes are formed of one of Indium Tin Oxide (ITO) and Indium ZincOxide (IZO).
 35. The method of claim 22, further comprising first andsecond alignment layers on the first and second substrates.
 36. Afabrication method of an in-plane switching mode liquid crystal displaydevice comprising: forming data lines and gate lines arranged in amatrix form on a first substrate to define a pixel; forming a thin filmtransistor at a cross portion of the gate and data lines, the thin filmtransistor including a gate electrode, a semiconductor layer, a sourceelectrode and a drain electrode; forming a black matrix over the gatelines, data lines, and the thin film transistor; forming a color filterlayer in the pixel; forming a storage electrode positioned under thecolor filter layer, the storage electrode is connected to the drainelectrode and the pixel electrode; forming an overcoat layer over thecolor filter layer; forming at least a pair of a common electrode and apixel electrode on the overcoat layer; and attaching a second substrate;and attaching the first substrate and a second substrate.
 37. The methodof claim 36, further comprising forming a first alignment layer on thefirst substrate.
 38. The method of claim 36, further comprising forminga second alignment layer on the second substrate.
 39. The method ofclaim 36, further comprising forming a liquid crystal layer between thefirst and second substrates.